The fervor over the digital currency bitcoin has drawn interest from two of the world's largest movers of money. Western Union Co. (WU) and MoneyGram International Inc. (MGI) are studying ways their customers could use their services to send and receive money transfers denominated in bitcoins, the companies' executives say. Both companies run remittance networks commonly used by immigrants to send money to friends and family members in foreign countries. Western Union also operates a business-solutions unit that sells services to companies for sending payments to other businesses. The firms have no immediate plans to add bitcoins as a currency option for customers, though both say the increasing popularity of the virtual money has prompted them to consider whether they should make it available in the future. "If bitcoin continues to grow and the value is defined more inter...